1. Field of the Invention
The present invention relates generally to internal valves for tanks, and more specifically refers to internal valves with locks for use in mobile tank cars.
2. Description of the Related Art
Tank valves are used for loading or unloading tanks, including railroad tank cars, truck tanks, stationary tanks, or other types of tanks used to contain liquids, gasses, or slurries. Applicant's U.S. Pat. No. 5,042,776 discloses an internal tank valve. The internal tank valve is positioned internally of the tank and is therefore less susceptible to damage, particularly in the event of a derailment or other accident involving a mobile tank. The internal tank valve disclosed in the '776 patent can be conveniently installed from the exterior of the tank, and easily removed for repair or replacement. The operator for the internal tank valve is also located internally of the tank.
Railroad tank cars and truck tanks are notoriously subjected to vibrations and shocks. Applicant's U.S. Pat. No. 5,145,151 discloses an internal tank valve with a valve lock to increase the safety factor of the valve. The internal tank valve of the '151 patent includes a primary seal which can be more securely locked in the closed position to assure a positive seal, a fire safe valve, and reduces the likelihood of spillage of material from inside of the tank in the event of a derailment or accident of the tank car. The locking structure is provided at a location that allows the valve to be held in a closed positive sealing position in the event of an accident in which part of the valve that protrudes and cap may be sheared off.
Applicant's U.S. Pat. No. 5,170,988 discloses an internal tank valve that is a cam actuated, quick acting, self-locking valve which reduces the possibility of the tank valve being opened due to shocks or vibration.
U.S. Pat. No. 5,342,026 discloses a valve having a cam actuator for opening and closing the valve. The cam actuator is directly coupled to a valve disk with a resilient coupling assembly.
Applicant's U.S. Pat. No. 5,931,444 discloses an internal tank valve having a safety lock for securely locking the valve in the closed position. The valve also includes a shear plane that allows the outer portion of the valve to be sheared off without affecting the integrity of the safety lock.
It is desirable to have an internal tank valve with a safety lock and interlock mechanism that is simple, reliable, safe, economical, and inherently protected against mechanical failure.